(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Text Book Of Mechanical Engineering"

772                            Appendix L

of compression. Such an engine uses the same substance over
and over again, and the cycle is strictly reversible, for we have
complete expansion to <r, and complete compression to a. Its

u

h:

k

lV,7

i

efficiency therefore is measured like the cycle of Carnot.
substance is water at a, and steam and water at other times.

he

P. 623. Ratio of Expansion in a Single Cylinder.—
As a result of many recent practical experiments, it is found that
a ratio of expansion of between 6 and 9 is the highest limit
which can be adopted with economy, though a ratio of 4 will
yield practically as good results.

P. 624. Theoretical Diagram.-—In order to make the cal-
culations from the preliminary diagram agree with practical
diagrams, Prof. Unwin introduces a fractional coefficient in the
formulge, which he calls the diagram factor, and which is deduced
from experimental results of engines similar to that under con-
sideration. The value of the factor varies from '85 to '95 in
good engines.

P. 637. Exhaust Lap.—In the case of a D valve, an early
cut-off to steam will catfse an early cut-off to exhaust (see Zeuner's
diagram, p. 660). In such a case, if a later compression point be
advisable, it may be necessary njpt only to eliminate exhaust lap
entirely, but actually to give a small opening to exhaust when the
valve is at mid stroke. Such opening is then termed negative lap,
and would be shewn on the steam circle in Fig. 653.